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Sampling & Sample SizeWeek 10
W. Rofianto, ST, MSi
Sampling
Population Element
Population
Census
Sampling frame
Why Sample?
Greater accuracy
Availability of elements
Greater speed
Samplingprovides
Lower cost
Sample Vs. Census
Conditions Favoring the Use of
Type of Study
Sample Census
1. Budget
Small
Large
2. Time available
Short Long
3. Population size
Large Small
4. Variance in the characteristic
Small Large
5. Cost of sampling errors
Low High
7. Nature of measurement
Destructive Nondestructive
8. Attention to individual cases Yes No
The Sampling Design Process
Define the Population
Determine the Sampling Frame
Select Sampling Technique(s)
Determine the Sample Size
Execute the Sampling Process
Classification of Sampling Techniques
Sampling Techniques
Nonprobability
Sampling TechniquesProbability
Sampling Techniques
Convenience
Sampling
Judgmental
Sampling
Quota
Sampling
Snowball
Sampling
Systematic
Sampling
Stratified
Sampling
Cluster
Sampling
OthersSimple Random
Sampling
Sample Size Determination
When estimating a population parameter by using a
sample statistic, the precision level is the desiredsize of the estimating interval. This is the maximumpermissible sampling error (difference between the samplestatistic and the population parameter).
The confidence interval is the range into which the truepopulation parameter will fall, assuming a given level ofconfidence.
The confidence level is the probability that aconfidence interval will include the population parameter.
Sample Size Determination for Means and Proportions
Steps Means Proportions
1. Specify the level of precision D = x - µ = $5.00 D = p - = 0.05
2. Specify the confidence level (CL) CL = 95% CL = 95%
3. Determine the z value associated with CL z value is 1.96 z value is 1.96
4. Determine the standard deviation of the
population
Estimate : = 55 Estimate : = 0.64
5. Determine the sample size using the formula for
the standard errorn = 2z2/D2 = 465 n = (1-) z2/D2 = 355
6. If the sample size represents 10% of the
population, apply the finite population correction
nc = nN/(N+n-1) nc = nN/(N+n-1)
7. If necessary, reestimate the confidence interval
by employing s to estimate = x zsx
= p zsp
8. If precision is specified in relative rather than
absolute terms, determine the sample size by
substituting for D.
D = Rµ
n = 2z2/(µR)2
D = R
n = z2(1-)/(R2)
LATIHAN
Pada suatu pre-test, terhadap sejumlah responden diperoleh
nilai rata-rata suatu variabel sebesar 1150 dengan standar
deviasi sebesar 200. Jika diinginkan tingkat presisi sebesar 40
pada confidence level sebesar 95%. Berapakah jumlah sampel
yang harus dipergunakan?
Improving Response Rates
Prior
Notification
Motivating
Respondents
Incentives Questionnaire
Design
and
Administration
Other
Facilitators
Callbacks
Methods of Improving
Response Rates
Reducing
RefusalsReducing
Not-at-Homes
Metode Penelitian Check List
3.1 Tipe dan Objek Penelitian
Tipe Penelitian
Unit Analisis
Periode penelitian
3.2 Metode Pengumpulan Data
Tipe Data
Teknik Sampling
Jumlah Sampel
3.3 Operasionalisasi Variabel
3.4 Metode Analisis Data
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